The decision between taking a small reward immediately or waiting for a larger reward later is a critical one faced by many creatures throughout their lives. This ability derives from an interaction between multiple decision-making systems and is related to self-control, and inversely related to addiction liability. Importantly, he balance between those systems changes over the lifespan, but the mechanism of that change is unknown. In rats, willingness to wait for a larger reward is usually measured by putting the two options into direct conflict, such as in the titrated delay task, in which the delay is titrated unil the two choices are equal. The problem with the titrated delay task as a means to study mechanism is that it does not generally titrate smoothly and cannot provide a complete discounting curve. We have developed a new spatial version of the titrated discounting task that titrates within a single session reliably and allows the direct measurement of discounting curve parameters across sessions. We propose to use this new discounting task to determine the changes in discounting rates across the lifespan.